North Korea puts rockets on standby as US official warns regime is no 'paper tiger'

Baengnyeong Island, home to 5,000 South Korean civilians, sits just 10 miles from the border with North Korea. Fearing an attack from the north, the island has become a fortress with fences, bomb shelters and mine fields. NBC's Ian Williams reports.

By Courtney Kube and Ian Johnston, NBC News

North Korea put its rocket units on standby Friday to attack U.S. military bases in South Korea and the Pacific, after repeated threats one day after two American stealth bombers flew over the Korean Peninsula in a military exercise.

A U.S. official warned that the isolated communist state is “not a paper tiger” and its reaction should not be dismissed as “pure bluster.”

According to South Korea's news agency, Yonhap, North Korea announced Saturday that it had entered a state of war against South Korea. "In a special statement, the North said it will deal with every inter-Korean issue in a wartime manner," Yonhap reported. NBC News could not immediately confirm.

The two Koreas have been in a technical state of war because their 1950-53 conflict ended under an armistice and not a peace treaty.

NBC's Andrea Mitchell examines North Korea's brewing threats and what they mean for neighboring South Korea.

According to North Korea's official KCNA news agency, the country's leader Kim Jong Un “judged the time has come to settle accounts with the U.S. imperialists in view of the prevailing situation” at a midnight meeting of top generals, Reuters reported.

The U.S. official emphasized the danger posed by North Korea’s military and the unpredictable nature of its 30-year-old leader.

“North Korea is not a paper tiger so it wouldn't be smart to dismiss its provocative behavior as pure bluster. What's not clear right now is how much risk Kim Jong Un is willing to run to show the world and domestic elites that he's a tough guy,” said the official, who asked not to be named. “His inexperience is certain -- his wisdom is still very much in question.”

'War for national liberation'The state-controlled KCNA also published an article that said the “opportunity for peacefully settling the DPRK-U.S. relations is no longer available as the U.S. opted for staking its fate. Consequently, there remains only the settlement of accounts by a physical means.” DPRK stands for Democratic People’s Republic of Korea, the North's official name.

“A battle to be fought by the DPRK against the U.S. will become a war for national liberation to defend the sovereignty and dignity of the country and, at the same time, a revolutionary war to defend the human cause of independence and the justice of the international community,” the article by “news analyst” Minju Joson said.

South Korea’s Yonhap news agency quoted a South Korean military official as saying that there had been “increased movement of vehicles and forces” at missile launch sites in the North. “We are closely watching possibilities of missile launches,” the unnamed official said.

North Korea routinely issues hostile statements but analysts have noted recent remarks have become more belligerent. In December, the North carried out a long-range rocket test and then detonated a nuclear bomb in a test earlier this year.

At a daily news briefing Friday, China’s Foreign Ministry spokesman Hong Lei said China was calling for an easing of tensions.

But some fear the situation could be getting out of control.

North Korea's young leader Kim Jong-un has issued almost daily threats, including the threat of nuclear strikes on Washington, D.C., and Seoul. In addition, Pyongyang has put its troops on combat readiness, warning that war "may break out at any moment." NBC's Ian Williams reports.

"It seems that Kim Jong Un is in the driving seat of a train that has been taken on a joyride," Lee Min-yong, an expert on North Korea at Sookmyung Women's University in Seoul, told Reuters.

Russia, meanwhile, appeared to criticize the U.S. over Thursday's bomber mission.

"We are concerned that alongside the adequate, collective reaction of the U.N. Security Council, unilateral action is being taken around North Korea that is increasing military activity," Foreign Minister Sergei Lavrov told reporters in Moscow, according to Reuters.

"The situation could simply get out of control; it is slipping toward the spiral of a vicious cycle," he said.